Aguila Technologies (San Marcos, CA) announced that Henkel-Loctite Corp. (Industry, CA) has purchased a license to Aguila's patents on a pre-applied flip chip underfill technology. The Aguila license provides Henkel-Loctite the right to provide wafer-applied flip chip underfill adhesives that will enable fabrication of flip chips at lower cost and increased yield by eliminating the conventional capillary underfill technique.

Aguila's work in the field of advanced flip chip packaging over the past few years has led to over a dozen patents ranging from wafer-level and flip chip processes to no-flow underfills. Aguila's invention provides for a two-portion, or two-level, fluxing adhesive underfill approach. It overcomes the problem of applying an underfill adhesive containing filler particles to a flip chip prior to assembly.

Conventional flip chip technology generally requires that flip chip assemblies be encapsulated with an adhesive, or underfill, to protect the tiny flip chip solder joints from thermal fatigue failure. Particulate fillers in conventional underfills are the essential ingredients that reduce the adhesive's expansion rate with temperature fluctuations. The reduced expansion allows the underfill to match the expansion of the chip's solder bumps, greatly reducing fatigue failures during thermal cycling.

However, the application of underfills to finished flip chip assemblies has historically been a limiting factor to production yield and assembly cost. Conventional underfills are applied through a capillary flow liquid dispensing operation that creates a number of production obstacles.

Ideally, underfills would be applied to flip chips prior assembly. Attempts to put the essential filler particles into no-flow underfills have generally resulted in poor solder wetting and reduced product yields. The filler particles interfere with the flip chip soldering operation. These problems have led to no-flow underfills with no filler particles, limiting their usefulness.

Aguila's two-portion pre-applied underfill eliminates the problem. One portion, constituting the majority of the underfill, is filled with the essential particles that reduce thermal expansion. A second portion comprises few or no filler particles. Yet, it is the second portion that provides the fluxing action during the flip chip soldering operation. This results in a pre-applied underfill that does not interfere adversely with the soldering operation.

Aguila's innovation provides two-portion underfills that are pre-applied to flip chips, either at the wafer level, after wafer sawing, or just prior to the assembly operation. Thus, it eliminates the tedious dispense operation after flip chips are assembled. The underfill may be applied to hundreds of chips at a single time at the wafer, instead of one at a time after assembly.

www.aguilatech.com

www.loctite.com

Copyright 2004, UP Media Group. All rights reserved.

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